How to set a function for error propagation

Hey, this is kinda my first try with

function

My aim is to code an automatic sequence for error propagation. E.g.

function [DeltaY] = equation(x)

With DeltaY being the solution and x an equation like x = a*b

As I said I have very little experience with functions, hence:

function [DeltaY] = equation(x)
DeltaY = sqrt((diff x,a)^2 * da^2 + (diff x,b)^2 * db^2)
end

does not work if I typ

equation(x)

Strikes me as I need to define a b da db seperately like

syms a b da db
x = a*b

But where to put it?

Answer 1

[SAA]

Yes you need to deinfe a b da and db either in the function or in your script before you call the function and also let them be inputs to your function

like this:

function [DeltaY] = equation(x,a,b,da,db)
DeltaY = sqrt((diff x,a)^2 * da^2 + (diff x,b)^2 * db^2)
end

[Niklas Kurz]

One question is bothering me concering my code:

function [DeltaY] = equation(a, b, da, db)
DeltaY = sqrt(diff(((a+b)/(b-a)),a)^2 * da^2 + diff(((a+b)/(b-a)),b)^2 * db^2);
end

It works quite well, but as long as I define a,b,da,db Matlab won't derive anymore. For example

equation(1, 2, 0.1, 0.1)

gives:

ans = []

How to tell Matlab to set in values after it derived? Is this only possible with

subs()